In recent years, mobile devices (electronic devices, more specifically, portable electronic devices) that include a screen (for example, liquid crystal screen) with a touch panel and are represented by mobile phones, smartphones, and media players, have been widely used. The mobile devices are in the process of becoming more multi-functioned, more compact, or thinner, and some of the mobile devices equipped with a proximity sensor that detects (senses) whether or not there is an object in proximity thereto are put on the market.
A proximity sensor and a calibration method thereof according to the related art are described with reference to FIGS. 8 to 11. FIG. 8 is a view for explaining an operation principle of a proximity sensor 900 of the related art. FIG. 9 is a view for explaining a problem of the proximity sensor 900. FIG. 10 is a functional block diagram illustrating a schematic configuration of the proximity sensor 900. FIG. 11 is a flowchart illustrating an example of a flow of calibration processing of the proximity sensor 900. Note that, LED light emission P in FIG. 9 indicates a pulse signal for causing a light emitting unit 901 to emit light.
There are proximity sensors of various systems as the proximity sensor 900 of the related art, and a proximity sensor 900 of a light detection system is used in many cases in a small-sized mobile terminal such as a mobile phone or a media player. As illustrated in FIG. 8, the proximity sensor 900 of the light detection system causes outgoing light L1 emitted from the light emitting unit 901 in the proximity sensor 900 to be reflected by an object OB and receives reflected light L2 by a light receiving unit 902 in the proximity sensor 900 to thereby determine that the object is in proximity.
Such proximity sensor 900 of the light detection system is often used by being incorporated in a housing 960 of a mobile phone 950 as illustrated in FIGS. 9 and 10. In this case, the outgoing light L1 emitted from the light emitting unit 901 may be reflected by the housing 960 and reflected light L3 from the housing 960 may be received by the light receiving unit 902 in some cases.
Here, an amount of the reflected light L3 when the outgoing light L1 emitted from the light emitting unit 901 is reflected by the housing 960 varies depending on individual mobile phones or use environments thereof. Thus, when the light receiving unit 902 receives the reflected light L3 from the housing 960, a detected distance may have an error or an erroneous operation may be caused due to the variation of the amount of the reflected light L3 based on the individuals.
Under such circumstances, it is strongly desired to realize a proximity sensor (object detecting device) that has similar characteristics under various mounting conditions. Note that, an example of an index indicating the characteristics includes a detection distance (a distance between an object to be detected and the proximity sensor, by which it is determined that the object to be detected is in proximity) or a rate of occurrence of an erroneous operation.
Note that, factors that vary the amount of the reflected light L3 depending on individuals of the mobile phone 950 or use environments thereof are considered to be as follows. That is, a cause in a manufacturing process when the mobile phone 950 is shipped from a plant, contamination or change of an inner structure of the mobile terminal 950 due to degradation over time, conditions (mounting conditions of the proximity sensor) such as a position where the proximity sensor 900 is mounted in the mobile phone 950 and a shape of a surface of the housing of the mobile phone 950, in which the proximity sensor 900 has been mounted, and the like vary among manufacturers and models. As a reason therefor, restriction on a physical appearance and a design of the mobile phone 950 (electronic device) is cited.
There has been a calibration method by a proximity sensor as a countermeasure to prevent an erroneous operation due to the reflected light L3 from the housing 960, and an example thereof is described in PTL 1.
An outline of a calibration method similar to the calibration method described in PTL 1 is described with reference to FIGS. 10 and 11.
Specifically, the mobile phone 950 includes the proximity sensor 900, a mobile control unit 951, and a display unit 952. The proximity sensor 900 includes the light emitting unit 901, the light receiving unit 902, an analog-to-digital conversion unit 903, a storage unit 904, and a sensor control unit 910.
The light emitting unit 901 is an infrared LED (light emitting diode) that receives current supplied from the sensor control unit 910 and emits infrared rays. The light receiving unit 902 receives the infrared rays (reflected light L2) emitted from the light emitting unit 901 and reflected by the object OB and generates current according to an amount of light received by photoelectric conversion. The generated current is output to the analog-to-digital conversion unit 903.
In the storage unit 904, a predetermined threshold is stored in advance, and the stored threshold is read by the sensor control unit 910 and the stored threshold is updated by the sensor control unit 910.
The analog-to-digital conversion unit 903 performs AD conversion (analog-to-digital conversion) on the current output from the light receiving unit 902 and outputs a value represented by a digital signal to the sensor control unit 910.
Every time outgoing/incoming call information indicating an outgoing call from the mobile phone 950 or an incoming call to the mobile phone 950 is input from the mobile control unit 951, the sensor control unit 910 supplies current to the light emitting unit 901 to cause the light emitting unit 901 to emit light. At this time, the sensor control unit 910 generates a new threshold in accordance with a current value output from the analog-to-digital conversion unit 903 and updates the threshold to be stored in the threshold storage unit 904. Such processing in sequence is referred to as calibration.
The sensor control unit 910 performing the calibration causes the light emitting unit 901 to emit light, compares the current value output from the analog-to-digital conversion unit 903 and the threshold (when the threshold has been updated, the updated threshold) read from the storage unit 904, and detects proximity of a user in accordance with a comparison result. When detecting proximity of the user, the sensor control unit 910 outputs detection information to the mobile control unit 951.
That is, every time there is an outgoing call from or an incoming call to the mobile phone 950, the proximity sensor 900 measures noise floor, performs the calibration, and then, detects proximity of an object (user), and outputs detection information indicating the proximity, to the mobile control unit 951 of the mobile phone 950. In a case where the detection information indicating the proximity of the user is input from the proximity sensor 900, the control unit 951 performs control, for example, to turn off a function of a touch panel and turn off display of the display unit 952.
Next, an example of a flow of calibration processing of the proximity sensor 900 is described with reference to FIG. 11.
First, the sensor control unit 910 determines whether or not outgoing/incoming call information is acquired from the mobile control unit 951 of the mobile phone 950 (S1001). When the outgoing/incoming call information is acquired (YES at S1001), the sensor control unit 910 supplies current to the light emitting unit 901 to cause the light emitting unit 901 to emit light (S1002), generates a new threshold in accordance with a current value output from the analog-to-digital conversion unit 903, and updates a threshold stored in the storage unit 904 (S1003). Calibration processing performed by the proximity sensor 900 when there is an outgoing call from or an incoming call to the mobile phone 950, that is, when the proximity sensor 900 is activated is indicated by S1001 to S1003. Note that, in a case where the outgoing/incoming call information is not acquired (NO at S1001), the procedure returns to S1001 to determine acquisition of the outgoing/incoming call information.
Next, the sensor control unit 910 supplies current to the light emitting unit 901 to cause the light emitting unit 901 to emit light (S1004), compares the current value output from the analog-to-digital conversion unit 903 and the threshold read from the storage unit 904, and determines whether or not the current value is equal to or higher than the threshold (S1005). In a case where the current value is equal to or higher than the threshold (YES at S1005), the sensor control unit 910 determines that a detection target in proximity is detected (S1006) and outputs detection information to the mobile control unit 951. In a case where the current value is less than the threshold (NO at S1005), the sensor control unit 910 determines that a detection target is in no proximity (S1007), and ends the processing.
As a result, by performing the calibration of the proximity sensor 900 when there is an outgoing call from or an incoming call to the mobile phone 950, for example, even when noise floor changes due to various external factors in an adjustment step before shipment from a plant, due to change in an inner structure over time, or the like, proximity of the user is able to be correctly detected.